Moisture Sources and Quantitative Analyses of Source Contributions of Precipitation Associated with Rammasun (1409)

Using the Flexible Particle (FLEXPART) model, a Lagrangian particle dispersion model, and the areal source-receptor attribution method, the moisture sources for super typhoon Rammasun (landfalling from 0600 UTC July 17, 2014 to 0600 UTC July 19, 2014) were studied, and the contributions from these moisture sources were quantified. Results indicated that the vast majority of the target particles were from southwest and east of the target precipitation region. The former originated from the relatively lower layers of the atmosphere and could be traced back to regions such as the Arabian Sea and the Bay of Bengal, and particle height did not change much in transit. The latter could be traced back to the Western Pacific Ocean, and the particles were relatively higher at their source, descending during transportation. The South China Sea region (C) made the largest contribution, followed by the target precipitation region (T), while the Bay of Bengal (B) and the southern Western Pacific region (D) both contributed similar amounts that were less than those from region T. The greater contributions of regions C and T to the precipitation during Rammasun landfall were attributed to their higher uptake by the storm (especially from region C) and reduced loss in transit (especially from region T). The uptake from region B was higher than that from region D, but the unreleased proportion from the former was significantly higher than that from the latter. Meanwhile, the moisture loss in transit to the storm from both regions B and D was equivalent, resulting in roughly equal contributions to the target precipitation area. Although uptake from the Arabian Sea region (A) was also substantial, its ultimate contribution to the target precipitation region was dramatically reduced due to evaporation in the air parcels. Our study demonstrated that the FLEXPART model and areal source to receptor attribution method can reveal relative moisture source contributions to tropical cyclone precipitation more clearly and quantitatively than the qualitative commonly-used circulation and water vapor flux analysis.